The present invention relates to developing devices providing a single component developing agent to an image carrier, as well as to image forming apparatuses such as copiers, printers, fax machines and the like provided with such a developing device.
As is disclosed in JP H02-221977A, image forming apparatuses, such as copiers, are provided with a developing device for supplying a single component developing agent (also referred to as “toner” in the following) to an image carrier, in order to develop a static latent image formed on the surface of the image carrier (photosensitive drum).
A developing device 100 in JP H02-221977A, as shown in FIG. 1, includes a developer 101, a toner supply roller 102, a developing roller 103 and a coating blade (layer regulating member) 104. Unused toner T serving as the developing agent is contained inside the developer 101,
To supply toner from the developing device 100 to the photosensitive drum 110 of the image forming apparatus, the unused toner T inside the developer 101 is transported to the developing roller 103 by rotating the toner supply roller 102. Then, the toner carried on the surface of the developing roller 103 is transported to a pressure contact region at which the coating blade 104 presses against the developing roller 103. At this pressure contact region, the toner T on the developing roller 103 is regulated to a suitable layer thickness by the coating blade 104 and is subjected to frictional charging, after which it is transported to a contact region where the photosensitive drum 110 contacts the developing roller 103 (developing nip region).
However, with the above-described configuration for regulating the layer thickness using this coating blade, the contact pressure of the coating blade on the development roller is large, so that an excessive load was applied to the toner by the pressure contact region. Therefore, there was the problem that the toner was degraded and the flow properties and charge properties deteriorated.
This leads to a decrease of the toner concentration due to a decrease of the toner amount transported by the roller and image fog or toner scattering due to the supplying of toner that is not properly charged to the contact region, thus decreasing image quality. Moreover, there was also the problem that toner was fused to the contact surface where the coating blade contacts the toner. This leads to white strikes or the like in the image formed on the paper.
To address this problem, it is conceivable to diminish the contact pressure with which the coating blade presses against the development roller, but if this contact pressure is diminished, then it is not possible to form a consistently thin toner layer, and if the toner amount per unit surface area becomes large, then this may lead to scattering of the toner during the development of the static latent image or during transfer onto the recording medium (also referred to below as “paper”), therefore degrading the image quality. In particular in image forming apparatuses with a configuration in which the pigment concentration of the toner is increased to attain a sufficient image density with a small amount of toner, the layer thickness of the toner is very important.
It is thus an object of the present invention to provide a developing device with which a single component developing agent with a layer thickness that is suitable for development can be supplied from the peripheral surface of an endless belt to the surface of an image carrier, while reducing the contact pressure of the layer regulating member pressing against the endless belt. It is also an object of the present invention to provide image forming apparatus provided with such a developing device.